Finfet with reduced capacitance

ABSTRACT

A structure including a gate electrode above and perpendicular to a plurality of semiconductor fins, a pair of spacers disposed on opposing sides of the gate electrode, and a gap fill material above a semiconductor substrate, directly below the gate electrode, and between the plurality of fins, the gate electrode separates the gap fill material from each of the plurality of fins.

BACKGROUND

The present invention generally relates to integrated circuits, and moreparticularly to reducing parasitic capacitance of a finFET semiconductordevice.

As integrated circuits continue to scale downward in size, a fin fieldeffect transistor (finFET) is becoming more widely used. A typicalfinFET device may be fabricated with either a gate first process flow ora gate last, or replacement gate, process flow. Typically, a gate firstprocess flow may include forming fins in a substrate, depositing a gatestack including a high-k dielectric and one or more gate metals, andfinally etching the final gate structures. Alternatively, a replacementgate (RG) process flow may include the use of a dummy gate stack. Inboth cases, a gate electrode of the final finFET structure may occupymost of the space between adjacent fins in a gate region of the finFET.Furthermore, an epitaxially grown region (EPI region) may be formedabove the ends of the fins not covered by the gate, for examplesource-drain regions. The EPI region may effectively merge thesource-drain regions of adjacent devices, and in doing so, may occupythe space between adjacent fins. Therefore, the space between adjacentfins in the source-drain regions may be occupied with EPI region, andthe space between adjacent fins in a gate region may be occupied by thegate electrode. In most cases, the source-drain regions may be coupledwith two opposite sides of the gate region, with a spacer toelectrically insulate the gate region from the source-drain regions.

The configuration of the EPI region and the gate electrode separated bythe spacer may unintentionally form a capacitive structure in which twoelectrical conductors are separated by an insulator. This configurationmay result in undesirable parasitic capacitance which may typically bereferred to as gate-to-EPI capacitance. The gate-to-EPI capacitance mayadd to the total capacitance associated with the device and reduce theswitching speed of the device.

Therefore, it may be desirable, among other things, to reduce thegate-to-EPI capacitance.

SUMMARY

According to one embodiment of the present invention, a method isprovided. The method may include a gate electrode above andperpendicular to a plurality of semiconductor fins, a pair of spacersdisposed on opposing sides of the gate electrode, and a gap fillmaterial above a semiconductor substrate, directly below the gateelectrode, and between the plurality of fins, the gate electrodeseparates the gap fill material from each of the plurality of fins.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the invention solely thereto, will best be appreciatedin conjunction with the accompanying drawings, in which:

FIG. 1 is an isometric view of a finFET structure according to the priorart.

FIG. 2 is a cross section view, section A-A, of FIG. 1.

FIGS. 3-19 illustrate the steps of a method of forming a finFETaccording to an exemplary embodiment.

FIG. 3 illustrates the formation of a plurality of fins formed from asemiconductor substrate according to an exemplary embodiment.

FIG. 4 illustrates the formation of a dummy gate oxide and a gap fillmaterial according to an exemplary embodiment.

FIG. 5 is a cross section view, section A-A, of FIG. 4.

FIG. 6 illustrates the formation of a plurality of dummy gate linesaccording to an exemplary embodiment.

FIG. 7 is a cross section view, section A-A, of FIG. 6.

FIG. 8 illustrates the formation of spacers on the sidewalls of theplurality of dummy gate lines according to an exemplary embodiment.

FIG. 9 is a cross section view, section A-A, of FIG. 8.

FIG. 10 illustrates the formation of an epitaxially grown region (“EPIregion”) according to an exemplary embodiment.

FIG. 11 is a cross section view, section A-A, of FIG. 10.

FIG. 12 illustrates the formation of a dielectric layer above the EPIregion according to an exemplary embodiment.

FIG. 13 is a cross section view, section A-A, of FIG. 12.

FIG. 14 illustrates the selective removal of a dummy gate according toan exemplary embodiment.

FIG. 15 is a cross section view, section A-A, of FIG. 14.

FIG. 16 illustrates the selective removal of the dummy gate oxideaccording to an exemplary embodiment.

FIG. 17 is a cross section view, section A-A, of FIG. 16.

FIG. 18 illustrates the formation of a gate electrode according to anexemplary embodiment.

FIG. 19 is a cross section view, section A-A, of FIG. 18.

FIGS. 20-27 illustrate the steps of a method of forming a finFETaccording to another exemplary embodiment.

FIG. 20 illustrates the formation of a plurality of dummy gate linesaccording to an exemplary embodiment.

FIG. 21 is a cross section view, section A-A, of FIG. 20.

FIG. 22 illustrates the selective removal of the dummy gate oxideaccording to an exemplary embodiment.

FIG. 23 is a cross section view, section A-A, of FIG. 22.

FIG. 24 illustrates the formation of an EPI region according to anexemplary embodiment.

FIG. 25 is a cross section view, section A-A, of FIG. 24.

FIG. 26 illustrates the formation of a dielectric layer according to anexemplary embodiment.

FIG. 27 is a cross section view, section A-A, of FIG. 26.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention. In the drawings, like numbering representslike elements.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it can be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of this invention to thoseskilled in the art. In the description, details of well-known featuresand techniques may be omitted to avoid unnecessarily obscuring thepresented embodiments.

The present embodiment relates generally to the fabrication of finFETdevices, and more particularly, to reducing the parasitic capacitancebetween a gate electrode and an epitaxially grown region (hereinafter“EPI region”). The gate electrode and the EPI region may be separated bya dielectric spacer and together may form the basic structure of acapacitor. It may be advantageous to minimize the parasitic capacitancebetween the gate electrode and the EPI region of a finFET device toreduce the total capacitance and improve switching speed.

A finFET device may generally include a plurality of fins formed in awafer, a gate covering a portion of the fins, where the portion of thefins covered by the gate serves as a channel region of the device andportions of the fins extending out from under the gate serve as sourceand drain regions of the device; and dielectric spacers on oppositesides of the gate that separate the gate from the source and drainregions. The present embodiment may be implemented in a gate lastfabrication process flow, and as such a gate last, or replacement gate(RG), process flow will be relied upon for the detailed descriptionbelow.

In a typical RG process flow, a semiconductor substrate may be patternedand etched to form fins. Either a bulk substrate or asemiconductor-on-insulator (SOI) substrate may be used. Next, a dummygate may be formed in a direction perpendicular to the length of thefins. For example, the dummy gate may be pattered and etched from ablanket layer of polysilicon. A pair of spacers can be disposed onopposite sidewalls of the dummy gate. Later, the dummy gate may beremoved from between the pair of spacers, as by, for example, ananisotropic vertical etch process such as a reactive ion etch (RIE).This creates an opening between the spacers where a high-k dielectricand gate electrode may then be formed.

By way of example FIGS. 1 and 2 illustrate a structure 100 of a finFET.It should be noted that FIG. 1 represents an isometric view havingmultiple cut-out sections intended to improve clarity and understanding.While FIG. 2 is a cross-section view, section A-A, of FIG. 1. It shouldbe noted, that the section A-A is a view of the structure 100 below atop surface of the fins 106 a-106 c.

Referring now to FIG. 1, the isometric view of the structure 100 isshown at an intermediate step during the process flow. At this step offabrication, the structure 100 may generally include the plurality offins 106 a-106 c, etched from a semiconductor substrate. Thesemiconductor substrate may include a bulk semiconductor or a layeredsemiconductor such as Si/SiGe, a silicon-on-insulator (SOI), or aSiGe-on-insulator (SGOI). Bulk semiconductor substrate materials mayinclude undoped Si, n-doped Si, p-doped Si, single crystal Si,polycrystalline Si, amorphous Si, Ge, SiGe, SiC, SiGeC, Ga, GaAs, InAs,InP and all other III/V or II/VI compound semiconductors. In theembodiment shown in FIG. 1 a SOI substrate may be used. The SOIsubstrate may include a base substrate 102, a buried dielectric layer104 formed on top of the base substrate 102, and a SOI layer (not shown)formed on top of the buried dielectric layer 104. The buried dielectriclayer 104 may isolate the SOI layer from the base substrate 102. Itshould be noted that the plurality of fins 106 a-106 c may be etchedfrom the uppermost layer of the SOI substrate, the SOI layer.

The base substrate 102 may be made from any of several knownsemiconductor materials such as, for example, silicon, germanium,silicon-germanium alloy, silicon carbide, silicon-germanium carbidealloy, and compound (e.g. III-V and II-VI) semiconductor materials.Non-limiting examples of compound semiconductor materials includegallium arsenide, indium arsenide, and indium phosphide. Typically thebase substrate 102 may be about, but is not limited to, several hundredmicrons thick. For example, the base substrate 102 may have a thicknessranging from 0.5 mm to about 1.5 mm.

The buried dielectric layer 104 may include any of several dielectricmaterials, for example, oxides, nitrides and oxynitrides of silicon. Theburied dielectric layer 104 may also include oxides, nitrides andoxynitrides of elements other than silicon. In addition, the burieddielectric layer 104 may include crystalline or non-crystallinedielectric material. Moreover, the buried dielectric layer 104 may beformed using any of several known methods, for example, thermal orplasma oxidation or nitridation methods, chemical vapor depositionmethods, and physical vapor deposition methods. The buried dielectriclayer 104 may have a thickness ranging from about 5 nm to about 200 nm.In one embodiment, the buried dielectric layer 104 may have a thicknessranging from about 150 nm to about 180 nm.

The SOI layer may include any of the several semiconductor materialsincluded in the base substrate 102. In general, the base substrate 102and the SOI layer may include either identical or differentsemiconducting materials with respect to chemical composition, dopantconcentration and crystallographic orientation. In one particularembodiment of the present invention, the base substrate 102 and the SOIlayer include semiconducting materials that include at least differentcrystallographic orientations. Typically the base substrate 102 or theSOI layer include a {110} crystallographic orientation and the other ofthe base substrate 102 or the SOI layer includes a {100}crystallographic orientation. Typically, the SOI layer may include athickness ranging from about 5 nm to about 100 nm. In one embodiment,the SOI layer may have a thickness ranging from about 25 nm to about 30nm. Methods for forming the SOI layer are well known in the art.Non-limiting examples include SIMOX (Separation by Implantation ofOxygen), wafer bonding, and ELTRAN® (Epitaxial Layer TRANsfer). It maybe understood by a person having ordinary skill in the art that theplurality of fins 106 a-106 c may be etched from the SOI layer. Becausethe plurality of fins 106 a-106 c may be etched from the SOI layer, theytoo may share any of the characteristics listed above for the SOI layer.

With continued reference to FIG. 1 and now referring also to FIG. 2, thestructure 100 may include multiple gate electrodes, for example a gateelectrode 108, formed on top of, and perpendicular to, the fins 106a-106 c. The gate electrode 108 may further include one or moredielectric spacers, for example spacers 110. The spacers 110 may beformed by conformally depositing or growing a dielectric, followed by ananisotropic etch that removes the dielectric from the horizontalsurfaces of the structure 100 and from vertical sidewalls of the fins106 a-106 c, while leaving it on the sidewalls of the gate electrode108. In a RG process flow the spacers 110 may remain on the sidewalls ofa dummy gate (not shown). In one embodiment, the spacers 110 may includeany suitable dielectric material such as silicon nitride. In oneembodiment, the spacers 110 may have a horizontal width, or thickness,ranging from about 3 nm to about 30 nm. The spacers 110 may include asingle layer; however, the spacers 110 may include multiple layers ofdielectric material. The spacers 110 may be positioned along thesidewalls of the gate electrode 108 and separate the gate electrode 108from an epitaxially merged source-drain region, for example an EPIregion 112. A dielectric layer 114 may fill any remaining space abovethe EPI region 112 and between the spacers 110.

The configuration of the gate electrode 108 and the EPI region 112separated by the spacer 110 may experience capacitive characteristics.(See FIG. 2). The spacer 110 may typically include a nitride, or othermaterial having a moderately high dielectric constant, and thereforeresult in undesirable parasitic capacitance within the structure 100.The parasitic capacitance may lower the switching speed of thetransistor. It may therefore be desirable to reduce or eliminate theparasitic capacitance described above.

Ideally, parasitic capacitance between any gate electrode and EPI regionmay preferably be reduced or eliminated for the reasons discussed above.One way to reduce the parasitic capacitance between a gate electrode andan EPI region may include reducing the amount of gate electrode materialin close proximity to the EPI region. One exemplary embodiment by whichto reduce the parasitic capacitance is described in detail below byreferring to the accompanying drawings in FIGS. 3-20. In the presentembodiment, a gap fill material may be incorporated into a typical RGprocess flow to effectively reduce the amount of gate electrode materialin close proximity to the EPI region.

Referring now to FIGS. 3-19, exemplary process steps of forming astructure 200 in accordance with one embodiment of the present inventionare shown, and will now be described in greater detail below. It shouldbe noted that FIGS. 3-19 all depict the structure 200 having a pluralityof fins 206 a-206 c formed in a semiconductor substrate. Furthermore, itshould be noted that while this description may refer to some componentsof the structure 200 in the singular tense, more than one component maybe depicted throughout the figures and like components are labeled withlike numerals. The specific number of fins depicted in the figures isfor illustrative purposes only.

Referring now to FIG. 3, an isometric view of the structure 200 is shownat an intermediate step during the process flow. At this step offabrication, the structure 200 may generally include the plurality offins 206 a-206 c, etched from a substrate. Like above, the semiconductorsubstrate may include a bulk semiconductor or a layered semiconductorsuch as Si/SiGe, a silicon-on-insulator (SOI), or a SiGe-on-insulator(SGOI). In the present embodiment, a SOI substrate may be used. The SOIsubstrate may include a base substrate 202, a buried dielectric layer204 formed on top of the base substrate 202, and a SOI layer (not shown)formed on top of the buried dielectric layer 204. The buried dielectriclayer 204 may isolate the SOI layer from the base substrate 202. Itshould be noted that the plurality of fins 206 a-206 c may be etchedfrom the uppermost layer of the SOI substrate, the SOI layer. The basesubstrate 202 and the buried dielectric layer 204 may be substantiallysimilar to the base substrate 102 and the buried dielectric layer 104,described above. Furthermore, the SOI layer, for example the pluralityof fins 206 a-206 c, may be substantially similar to the SOI layer andthe plurality of fins 106 a-106 c, described above. The fins 206 a-206 cmay have a width (w) and be spaced by a distance (s), as shown in thefigure. In one embodiment, the width (w) of the fins 206 a-206 c may beabout 10 nm and the fins 206 a-206 c may be spaced by a distance (s) ofabout 30 nm to about 50 nm, as measured from the edge of one fin to theedge of another fin.

Referring now to FIG. 4, the isometric view of the structure 200 isshown after the deposition of a dummy gate oxide 208 and a gap fillmaterial 210. The dummy gate oxide 208 may include any suitable oxide,for example, a silicon oxide or a silicon oxynitride. In a preferredembodiment, the dummy gate oxide 208 may include any material that whichmay be removed selective to the gap fill material 210. The dummy gateoxide 208 can be deposited using any suitable conformal depositiontechnique known in the art. In one embodiment, the dummy gate oxide 208may include silicon dioxide (SiO₂) deposited using a chemical vapordeposition technique. The dummy gate oxide 208 may have a thickness lessthan about half of the spacing (s) (FIG. 3) between two adjacent fins,for example the fins 206 a-206 c. In one embodiment, the dummy gateoxide 208 may have a thickness ranging from about 5 nm to about 10 nm,although a thickness less than 5 nm and greater than 10 nm may beacceptable.

The gap fill material 210 may include any suitable nitride, for example,a silicon nitride. In a preferred embodiment, the gap fill material 210may include any material that which may have a considerably slower etchrate than the dummy gate oxide 208 described above. The gap fillmaterial 210 can be deposited using any suitable deposition techniqueknown in the art. In one embodiment, the gap fill material 210 mayinclude silicon nitride (Si₃N₄) deposited using a chemical vapordeposition technique. In one embodiment, the gap fill material 210 maybe deposited with a conformal deposition technique such as chemicalvapor deposition (CVD) or plasma enhanced CVD (PECVD) and polished usingfor example chemical mechanical polishing (CMP) to a height determinedby the dummy gate oxide 208 above the fins 206 a-206 c. In oneembodiment, the gap fill material 210 may be subsequently etched back tothe desired height with a reactive ion etching (RIE) technique. Inanother embodiment, the gap fill material 210 can be deposited with adeposition technique that may form a thicker material at the bottom ofthe opening formed between the dummy gate oxide 208 for example using ahigh-density plasma (HDP) CVD method. A top surface of the gap fillmaterial 210 may be substantially flush with a top surface of the fins206 a-206 c, although a height above or below the top surface of thefins 206 a-206 c may be acceptable.

Referring now to FIG. 5, a cross section view, section A-A, of FIG. 4 isshown. Again, it should be noted, that the section A-A is a view of thestructure 200 below the top surface of the fins 206 a-206 c. The spacebetween adjacent fins, for example the fin 206 a and the fin 206 b, maybe filled with the dummy gate oxide 208 and the gap fill material 210.Where the fins 206 a-206 c may be in direct contact with only the dummygate oxide 208, and the gap fill material 210 may be in direct contactwith the dummy gate oxide 208.

Referring now to FIG. 6, the isometric view of the structure 200 isshown after the formation of multiple dummy gate lines 212. The dummygate lines 212 may be formed by depositing a dummy gate 214 followed bya dummy gate cap 216. The dummy gate 214 may include any suitablesilicon or polysilicon able to be selectively removed. In oneembodiment, the dummy gate 214 may include amorphous silicon. The dummygate 214 may be deposited using typical deposition techniques, forexample, atomic layer deposition (ALD), molecular layer deposition(MLD), chemical vapor deposition (CVD), physical vapor deposition (PVD),and spin on techniques. In one embodiment, the dummy gate 214 may have athickness, or height, above the dummy gate oxide 208 ranging from about30 nm to about 100 nm, and ranges there between.

The dummy gate cap 216 may include any suitable dielectric materialknown in the art, for example, a nitride. The dummy gate cap 216 mayalso be deposited using typical deposition techniques, for example,atomic layer deposition (ALD), molecular layer deposition (MLD),chemical vapor deposition (CVD), physical vapor deposition (PVD), andspin on techniques. In one embodiment, the dummy gate cap 216 mayinclude silicon nitride (Si₃N₄) deposited using a chemical vapordeposition technique. In one embodiment, the dummy gate cap 216 may havea thickness ranging from about 10 nm to about 50 nm and ranges therebetween, although a thickness less than 10 nm and greater than 50 nm maybe acceptable.

The dummy gate 214 and the dummy gate cap 216 may then be patterned intothe dummy gate lines 212 by any suitable lithography technique known inthe art. In one embodiment, the dummy gate lines 212 may have a width(w), as measured in a direction parallel with the fins 206 a-206 c. Thewidth (w) may range from about 20 nm to about 200 nm, although lesser orgreater values can be used. The presence of the gap fill material 210may advantageously facilitate the patterning of the dummy gate lines 212because the dummy gate oxide 208 and the gap fill material 210 producelower variations in height as compared to a structure without the gapfill material 210. In the present embodiment, some of the dummy gateoxide 208 and some of the gap fill material 210 may preferably beremoved during the patterning of the dummy gate lines 212, and therebyexpose portions of the fins 206 a-206 c. It should be noted that thearea of the structure 200 covered by the dummy gate lines 212 maygenerally be referred to as a gate region, and the areas of thestructure 200 not covered by the dummy gate lines 212 may generally bereferred to as a source-drain region.

Referring now to FIG. 7, a cross section view, section A-A, of FIG. 6 isshown. The technique used to pattern the dummy gate lines 212 and removeportions of the dummy gate oxide 208 and the gap fill material 210 mayfurther expose the buried dielectric layer 204 and form a pocket 218 inthe source-drain regions of the structure 200. The pocket 218 may havetwo opposite sides defined by two adjacent fins and the other twoopposite sides defined by two adjacent dummy gate lines 212.

Referring now to FIG. 8, the isometric view of the structure 200 isshown after one or more spacers 220 are formed on the sidewalls thedummy gate lines 212. The spacers 220 may be formed by conformallydepositing or growing a dielectric material, followed by an anisotropicetch that removes the dielectric from the horizontal surfaces of thestructure 200 as well as the sidewalls of the fins 206 a-206 c whileleaving it on the sidewalls of the dummy gate lines 212. In oneembodiment, the spacers 220 may include any suitable dielectric. In oneembodiment, the spacers 220 may include silicon nitride. In oneembodiment, the spacers 220 may have a horizontal width, or thickness,ranging from about 3 nm to about 30 nm, with 10 nm being most typical.In one embodiment, the spacers 220 may include a similar material as thedummy gate cap 216. Typically, the spacers 220 may include a singlelayer; however, the spacers 220 may include multiple layers ofdielectric material. It may be noted that the spacers 220 may generallyinsulate the gate regions from the source-drain regions.

Referring now to FIG. 9, a cross section view, section A-A, of FIG. 8 isshown. The spacers 220 formed on the sidewalls of the dummy gate lines212 may redefine the boundaries of the pocket 218. The pocket 218 maynow have two opposite sides defined by two adjacent fins 206 a-206 c andthe other two opposite sides defined by two adjacent spacers 220. It maybe noted that below the top surface of the fins 206 a-206 c, the dummygate lines 212 may include the dummy gate oxide 208 and the gap fillmaterial 210. Therefore, in the gate regions, the fins 206 a-206 c maybe separated by the dummy gate oxide 208 and the gap fill material 210.During the current step, nothing may separate the fins 206 a-206 c fromone another in the source-drain regions.

Referring now to FIG. 10, the isometric view of the structure 200 isshown after an EPI region 222 may be grown on top of the plurality offins 206 a-206 c exposed in the source-drain regions. The portion of thefins 206 a-206 c exposed in the source-drain regions of the structure200 may be either n-doped or p-doped, and function as a source or drainof a resulting finFET device. Typically, n-doped source-drains are usedfor forming n-channel field effect transistors (n-FETs), and p-dopedsource-drains are used for forming p-channel field effect transistors(p-FETs). However, the source-drains of one device on a semiconductorsubstrate may be n-doped while the source-drains of another device onthe same semiconductor substrate may be p-doped. Methods well known inthe art may be use to implant the source-drains either before, during orafter growing the EPI region 222. Thus the EPI region 222 may be dopedafter being grown on the portion of the fins 206 a-206 c exposed in thesource-drain regions of the structure 200. In cases where both n-FETsand p-FETs are desired, masking materials, such as, for example,photoresist, SiO₂, Si₃N₄ or HfO₂, may be used to distinguish between thetwo different types of devices during the formation of the dopedsource-drain regions.

The EPI region 222 may be grown using any suitable technique known inthe art. For example, the EPI region 222 may be grown at a temperatureranging from about 700° C. to about 1000° C., for example using a CVD,low-pressure (LP) CVD, ultra-high vacuum (UHV) CVD or any method knownin art in conjunction with a silane, dichlorosilane, germane or othersuitable precursor gas. The EPI region 222 may be doped in-situ, forexample, by adding AsH₃, PH₃, or BH₃ to the gas mixture. Alternatively,in one embodiment, the EPI region 222 may be doped with a first typedopant, while the fins 206 a-206 c may be doped with a second typedopant. In-situ doping refers to the doping technique in which thedopants are introduced into the EPI region 222 at the same time the EPIregion 222 is being grown. In-situ doping may be attractive because thedopant distribution can be uniform throughout the region if the dopantis incorporated during and along with the growth of the EPI region 222.In one embodiment, the EPI region 222 may have a thickness ranging fromabout 5 nm to about 20 nm, with a doping concentration within a range ofabout 5×10¹⁹ atoms per cm³ to about 1×10²¹ atoms per cm³.

Referring now to FIG. 11, a cross section view, section A-A, of FIG. 10is shown. The pocket 218 (FIG. 9) in the source-drain regions of thestructure 200 may be substantially filled with the EPI region 222.Therefore, the EPI region 222 occupies the open space (i.e. the pocket218 of FIG. 9) between adjacent dummy gate lines 212. Also, it should benoted that only the spacers 220 may separate the dummy gate lines 212from the EPI region 222. More specifically, only the spacers 220 mayseparate the dummy gate oxide 208 and the gap fill material 210 from theEPI region 222.

Referring now to FIG. 12, the isometric view of the structure 200 isshown after the formation of a dielectric layer 224. The dielectriclayer 224 may generally be deposited above the EPI region 222 in thesource-drain regions of the structure 200. The dielectric layer 224 mayinclude any suitable dielectric material, for example, silicon oxide(SiO₂), silicon nitride (Si₃N₄), hydrogenated silicon carbon oxide(SiCOH), silicon based low-k dielectrics, or porous dielectrics. Knownsuitable deposition techniques, such as, for example, atomic layerdeposition, chemical vapor deposition, plasma enhanced chemical vapordeposition, spin on deposition, or physical vapor deposition may be usedto form the dielectric layer 224. Next, a chemical mechanical polishingtechnique may be applied to remove excess material from a top surface ofthe structure 200 and expose the dummy gate 214. The chemical mechanicalpolishing technique may remove substantially all of the dummy gate cap216 selective to the dummy gate 214.

Referring now to FIG. 13, a cross section view, section A-A, of FIG. 12is shown. The cross section view may not reveal any change in thestructure 200 after the addition of the dielectric layer 224 as the viewis shown from below the EPI region 222.

Referring now to FIG. 14, the isometric view of the structure 200 isshown after the dummy gate 214 may be substantially removed from thegate region of the structure 200. The dummy gate 214 may be removedselective to the dummy gate oxide 208 and the gap fill material 210.Furthermore, the chosen dielectric layer 224 may be resistant to theetching technique chosen to remove the dummy gate 214. The selectiveremoval of the dummy gate 214 may be accomplished by using any knownetching technique suitable to remove polysilicon selective to siliconoxide and silicon nitride. In one embodiment, for example, the dummygate 214 may be removed using a dry etching technique, for examplereactive ion etching.

Referring now to FIG. 15, a cross section view, section A-A, of FIG. 14is shown. The cross section view may not reveal any change in thestructure 200 after the removal of the dummy gate 214 as the view isshown from below the dummy gate 214.

Referring now to FIG. 16, the isometric view of the structure 200 isshown after the dummy gate oxide 208 may be substantially removed fromthe gate regions of the structure 200. The dummy gate oxide 208 may beremoved selective to the gap fill material 210, and the plurality offins 206 a-206 c. Furthermore, removal of the dummy gate oxide 208 mayexpose a portion of the buried dielectric layer 204, in the gate regionof the structure 200. The selective removal of the dummy gate oxide 208may be accomplished by using any known etching technique suitable toremove silicon oxide selective to silicon nitride, and silicon. In oneembodiment, for example, the dummy gate oxide 208 may be removed using adry etching technique, for example reactive ion etching.

In the present embodiment, the dielectric layer 224, the spacers 220,the plurality of fins 206 a-206 c, and the gap fill material 210 may allfunction as self-aligned masks. A portion of the dummy gate oxide 208may remain beneath the gap fill material 210 due to the placement of thegap fill material 210, and the anisotropic nature of the chosen etchingtechnique. The remaining portion of the dummy gate oxide 208 and the gapfill material 210 may be positioned between two adjacent fins, forexample 206 b and 206 c, and define one or more openings 226. Therefore,openings 226 may be positioned between the fins 206 a-206 c and the gapfill material 210 in the gate regions of the structure 200. The width(x) of the openings 226, as measured from the gap fill material 210 to afin, may be approximately equal to the thickness of the dummy gate oxide208.

Referring now to FIG. 17, a cross section view, section A-A, of FIG. 16is shown. The openings 226 in the gate region of the structure 200 areshown between a fin, for example the fin 206 b, and the gap fillmaterial 210. As mentioned above, the buried dielectric layer 204 may beexposed at the bottom of the openings 226.

Referring now to FIG. 18, the isometric view of the final structure 200is shown. Typical replacement gate fabrication techniques well known inthe art may be used to form a gate electrode 228 and complete theformation of the structure 200. In one embodiment, a gate oxide (notshown) may be deposited prior to forming the gate electrode 228. Thegate oxide may include any of the high-k dielectric materials known inthe art, for example HfO₂, and deposited with methods such as atomiclayer deposition (ALD), chemical vapor deposition (CVD), or physicalvapor deposition (PVD). The gate electrode 228 may include one or morework function metals such as TiN, TaN, or TiC, to achieve the desireddevice threshold voltage and one or more low resistance metal such as W,Al, or Co. The gate electrode 228 may substantially fill the openings226 (FIG. 16), and substantially cover and surround the gap fillmaterial 210. Formation of the gate electrode 228 between adjacent finsmay be limited to the openings 226 (FIG. 16) due to the placement of thegap fill material 210.

Referring now to FIG. 19 a cross section view, section A-A, of FIG. 18is shown. It should be noted, again, that the section A-A is a view ofthe structure 200 below the top surface of the fins 206 a-206 c. In thepresent embodiment, the gate electrode 228 may be deposited along thesidewalls of the fins 206 a-206 c where it may be most functional to theoperation of the finFET device. The thickness of the dummy gate oxide208 may dictate the width (x) of the openings 226 (FIG. 16) and thus thewidth (z) of the gate electrode 228. Therefore, the thickness of thedummy gate oxide 208 may be chosen specifically to accommodate a high-kgate oxide and a suitable thickness of the work function metal of thegate electrode 228. Since the threshold voltage of the transistordepends on the thickness of the work function metal among otherparameters, the fact that the thickness of the work function metal ispre-determined by the thickness of the dummy gate oxide 208 mayadvantageously reduce the variability in the threshold voltage of theresulting transistor.

Below the top surface of the fins 206 a-206 c, the gate electrode 228does not extend from one fin to the adjacent fin, like the gateelectrode 108 of FIG. 2. The location and placement of the gap fillmaterial 210 may substantially reduce the amount of gate electrode 228deposited between two adjacent fins. Reducing the amount of gateelectrode 228 between the fins may effectively reduce the parasiticcapacitance exhibited by similar structures without the gap fillmaterial 210. See FIG. 2. As described above, a capacitor may includetwo electrical conductors separated by an insulator, and decreasing thesize of one of the two electrical conductors may reduce the capacitancebetween the two electrodes. Therefore, if the EPI region 222 and thegate electrode 228 are electrical conductors separated by one spacer220, an insulator, reducing of the amount of gate electrode 228 betweenthe fins, effectively decreases the size of one of the two electrodesand may reduce the capacitance between the gate electrode 228 and theEPI region 222.

Another exemplary embodiment by which to reduce the parasiticcapacitance is described in detail below by referring to theaccompanying drawings in FIGS. 20-27. In the present embodiment, a gapfill material may be incorporated into a typical RG process flow toeffectively reduce the EPI region in close proximity to the gateelectrode. It should be noted that the process and techniques describedabove with reference to FIGS. 3-5 may be applied directly to the presentembodiment and the following embodiment and corresponding descriptionwill build on the above description.

Referring now to FIG. 20, the isometric view of the structure 200 isshown after the formation of multiple dummy gate lines 212, similar tothat described above. Similar deposition and etching techniques as thosedescribed above may be used to form the dummy gate lines 212. Unlike theabove embodiment, the dummy gate oxide 208 and the gap fill material 210may not be removed during patterning of the dummy gate lines 212. Thedummy gate lines 212 may be pattered selective to the dummy gate oxide208 and the gap fill material 210. Therefore, in the present embodiment,the fins 206 a-206 c may remain covered by the dummy gate oxide 208 andthe gap fill material 210. Furthermore, the spacers 220 may be formed onthe sidewalls of the dummy gate lines 212, like above.

Referring now to FIG. 21, a cross section view, section A-A, of FIG. 20is shown. The technique used to pattern the dummy gate lines 212 mayleave both the dummy gate oxide 208 and the gap fill material 210substantially untouched. FIG. 21 of the present embodiment may bedistinguished from FIG. 7 of the previously described embodiment, inthat the buried dielectric layer 204 may remain substantially covered bythe dummy gate oxide 208 and the gap fill material 210 in FIG. 21.

Referring now to FIG. 22, the isometric view of the structure 200 isshown after the dummy gate oxide 208 may be substantially removed fromthe source-drain regions of the structure 200 selective to the gap fillmaterial 210, and the plurality of fins 206 a-206 c. Like above, similartechniques as those described above may be used to remove the dummy gateoxide 208, and expose a portion of the buried dielectric layer 204.

In the present embodiment, the spacers 220, the dummy gate cap 216 theplurality of fins 206 a-206 c, and the gap fill material 210 may allfunction as self-aligned masks. Like above, a portion of the dummy gateoxide 208 may remain beneath the gap fill material 210 due to theplacement of the gap fill material 210, and the anisotropic nature ofthe chosen etching technique. The remaining portion of the dummy gateoxide 208 and the gap fill material 210 may be positioned between twoadjacent fins, for example 206 b and 206 c, and define one or moreopenings 230. Therefore, openings 230 may be positioned between the fins206 a-206 c and the gap fill material 210 in the source-drain regions ofthe structure 200. Unlike the openings 226 above, the openings 230 maybe formed adjacent to the dummy gate lines 212 and not beneath the dummygate lines 212. The width (y) of the openings 230, as measured from thegap fill material 210 to the fins 206 a-206 c, may be approximatelyequal to the thickness of the dummy gate oxide 208.

Referring now to FIG. 23, a cross section view, section A-A, of FIG. 22is shown. The openings 230 in the source-drain regions of the structure200 are shown between a fin, for example the fin 206 b, and the gap fillmaterial 210. As mentioned above, the buried dielectric layer 204 may beexposed at the bottom of the openings 230.

Referring now to FIG. 24, the isometric view of the structure 200 isshown after an EPI region 222 may be grown in the openings 230 (FIG. 22)and on top of the plurality of fins 206 a-206 c exposed in thesource-drain regions of the structure 200. Growth of the EPI region 222may be limited by the portion of the dummy gate oxide 208 and the gapfill material 210 remaining in the source-drain regions of the structure200. Like above, methods well known in the art may be use to implant thesource-drains either before, during or after growing the EPI region 222.It should be noted, the EPI regions 222 may be faceted (as depicted) ifa faceted epitaxial growth process is used. In such cases, the epitaxialgrowth slows down significantly of a certain crystallographic plane, forexample, {111}planes are formed. Alternatively, a conformal epitaxialgrowth technique may be used to yield a more conformal formation.Epitaxial growth methods and conditions to form either a faceted or anon-faceted epitaxial layer are known in the prior art.

Referring now to FIG. 25, a cross section view, section A-A, of FIG. 24is shown. The openings 230 (FIG. 9) in the source-drain regions of thestructure 200 may be substantially filled with the EPI region 222.Therefore, it may be evident from the figure, that the EPI region 222 issmaller as a result of the gap fill material 210. See FIG. 11 for acomparison.

Referring now to FIG. 26, the isometric view of the final structure 200is shown. The steps described in detail above with reference to FIGS.12-19 may be followed to achieve the final structure as illustrated inthe figure. First, the dielectric layer 224 may be deposited followed bya chemical mechanical polishing technique, as described above. Next, thedummy gate 214 may be removed and replaced with the gate electrode 228,as described above. It should be noted that typical RG fabricationtechniques may be used to achieve the final structure illustrated in thefigure. In the present embodiment, both the gate electrode 228 and theEPI region 222 may be limited due to the placement of the gap fillmaterial 210. In one embodiment, typical RG processing may allow for thegate electrode 228 to fill the space between adjacent fins and placementof the gap fill material 210 may only limit the EPI region 222.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A structure comprising: a gate electrode aboveand perpendicular to a plurality of semiconductor fins; a pair ofspacers disposed on opposing sides of the gate electrode; and a gap fillmaterial above a semiconductor substrate, directly below the gateelectrode, and between the plurality of fins, wherein the gate electrodeseparates the gap fill material from each of the plurality of fins. 2.The structure of claim 1, further comprising: an epitaxially grownregion (“EPI region”) above and between a portion of the plurality offins not covered by the gate electrode, wherein the pair of spacersisolates the EPI region from the gate electrode.
 3. The structure ofclaim 2, further comprising: a dielectric layer above the EPI region. 4.The structure of claim 1, further comprising: a dummy gate oxidedirectly above the semiconductor substrate and directly below the gapfill material, wherein the gate electrode separates the dummy gate oxidefrom each of the plurality of fins.
 5. The structure of claim 4, whereinthe semiconductor substrate comprises a semiconductor-on-insulatorsubstrate, and the dummy gate oxide is directly on top of an insulatorlayer of the semiconductor-on-insulator substrate.
 6. The structure ofclaim 1, wherein a top surface of the gap fill material is substantiallyflush with or below a top surface of the plurality of fins.
 7. Thestructure of claim 1, wherein the gap fill material comprises a nitride.8. The structure of claim 1, wherein the gap fill material is surroundedon two opposite sides by a pair of sidewall spacers.
 9. The structure ofclaim 1, wherein a lateral thickness of a portion of the gate electrodelocated between the gap fill material and at least one of the pluralitysemiconductor fins is approximately equal to a distance between the gapfill material and the at least one of the plurality of semiconductorfins.
 10. The structure of claim 1, wherein the gap fill material isbetween the pair of spacers.